This invention relates to an output control device for use in producing an output signal in response to an input signal, such as an audio signal or a video signal.
In general, it often happens that an input signal, such as an audio or a video signal, is subjected to fade-in or fade-out operation and is produced as an output signal which gradually increases or decreases a tone or an image. In order to realize the fade-in or the fade-out operation, an output control device is included in an audio or a video circuit.
A conventional output control device of the type described is supplied with a fade control signal along with the input signal. Specifically, the fade control signal has a preselected amplitude and is delivered to a time constant circuit which has a predetermined time constant. As a result, a variable amplitude signal is sent from the time constant circuit to an output control circuit during the fade-in or the fade-out operation.
Herein, it is noted that the output control circuit produces a control signal of an invariable level in the absence of the variable amplitude signal. Responsive to the control signal of the invariable level, an amplifier which is given the input signal produces the output signal determined by the invariable level.
On the other hand, when the variable amplitude signal is given from the time constant circuit to the output control circuit, the output control circuit produces the control signal which has a variable amplitude determined by the variable amplitude signal sent from the time constant circuit. Supplied with the control signal of the variable amplitude, the amplifier produces the output signal which has a variable amplitude determined by the control signal.
Herein, it should be noted that the amplitude of the output signal is varied at a constant rate determined by the time constant of the time constant circuit. This means that the fade-in or the fade-out operation is progressive at a constant speed determined by the time constant, which might make a certain person feel uneven.
In addition, a muting operation which quickly mutes a tone can not be realized by the use of the above-mentioned output control device because the tone is varied only at the rate determined by the time constant.